Influences of material defects and temperature on current-driven domain wall mobility

Abstract

Current-induced domain wall motion, which has potential application in the next-generation data storage and logic device, has attracted much interest in recent years. However, how the material defect and its joule heat influence current-driven domain wall motion in magnetic nanostripe is still unclear. This paper is to deal with these issues by using the Landau-Lifshitz-Gilbert spin dynamics. The results show that the material defect can pin domain wall motion and this pinning effect strongly depends on the defect concentration, location and shape. The pinning effect induced by the defect on domain wall motion results in the increase of threshold current, and the domain wall moves steadily and continuously. Specifically, the probability for domain wall motion induced by pinning effect is nonlinearly increasing with the increase of defect concentration. Namely, the increasing of the pinning ability with the increase of the defect concentration becomes fades away. Initially, when the defect is near to domain wall, the pinning ability is obvious. However, the pinning ability is not linearly increasing with the decrease of the initial distance between the defect and the domain wall. The results also show that the single defect is larger, the probability for domain wall motion induced by defect pining is bigger. Moreover, the material defect can suppress the domain wall trending toward breakdown and make domain wall move faster, but the suppressing ability is not obviously increasing with the increase of the defect concentration. On the other hand, the temperature field can remove the pinning phenomenon, which will result in the threshold current decrease. The decrease of the threshold current is of benefit to the working of the data storage and logic device. Also the temperature field can suppress the domain wall trending toward breakdown, but the suppressing ability is less than that of the defect. In addition, the Joule heat around defects can obviously eliminate the pinning effect of the defects, so the pinning effect for a few defects on current-induced domain wall motion can be ignored. Further analysis indicates that these effects are due to the change of the out-of-plane magnetization of the domain wall induced by the material defects and the temperature field, because the velocity of the domain wall motion induced by the applied current greatly depends on the out-of-plane magnetization of the domain wall.